Everything looks correct but I can't get my networks to talk

[IT_Spencer]

I have everything set up to start a network migration, but I can't get devices to talk across the networks. I currently have everything on a 192.168.4.0 subnet in my main location, on one of my satellite offices I have 192.168.54.0 subnet. Both of these talk right now without issue. 

We are migrating to a schema using 10.x.x.x network, and I have in the location with the 192.168.54.0 subnet set up a 10.5.4.0 subnet to replace the first. However, when I put devices on the replacement subnet they act like they can't see anything.

In my main location with the 192.168.4.0 I have a subnet setup that is 10.0.4.0

I need help in troubleshooting these. I came here because I've been on hold for several hours, and I have some people on-site that really want to go home.

Sites have VPNs using site-to-site. Due to a license error, they are both Meraki devices but in different organizations.

[cmr]

Can the 192.168.4.0 devices at the main location talk to the 10.0.4.0 devices?

If not then:

• Do you have two VLANs, one for each subnet?
• Do you have an IP (layer 3) interface on each VLAN?
• Do the devices in each VLAN have their default gateway pointing to the IP interface address?

In general what equipment do you have, MX, switches (models?) etc.? 

[OVERKILL]

Need some more details, as @cmr noted, how are you configuring the 2nd subnet? How are you putting devices on it, changing the access VLAN of the switch port?